The preRC protein ORCA organizes heterochromatin by assembling histone H3 lysine 9 methyltransferases on chromatin

Sumanprava Giri, Vasudha Aggarwal, Julien Pontis, Zhen Shen, Arindam Chakraborty, Abid Khan, Craig Mizzen, Kannanganattu V. Prasanth, Slimane Ait-Si-Ali, Taekjip Ha, Supriya G. Prasanth

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


Heterochromatic domains are enriched with repressive histone marks, including histone H3lysine 9 methylation, written by lysine methyltransferases (KMTs). The pre-replication complex protein Origin Recognition Complex-Associated (ORCA/LRWD1) preferentially localizes to heterochromatic regions in post-replicated cells. Its role in heterochromatin organization remained elusive. ORCA recognizes methylated H3K9 marks and interacts with repressive KMTs, including G9a/GLP and Suv39H1 in a chromatin context-dependent manner. Single33 molecule pull-down assays demonstrate that ORCA-ORC and multiple H3K9 KMTs exist in a single complex and that ORCA stabilizes H3K9 KMT complex. Cells lacking ORCA show alterations in chromatin architecture, with significantly reduced H3K9 di- and tri-methylation at specific chromatin sites. Changes in heterochromatin structure due to loss of ORCA affects replication timing, preferentially at the late-replicating regions. We demonstrate that ORCA acts as a scaffold for the establishment of H3K9 KMT complex and its association and activity at specific chromatin sites is crucial for the organization of heterochromatin structure.

Original languageEnglish (US)
Article numbere06496
Pages (from-to)1-54
Number of pages54
Issue number4
StatePublished - Apr 29 2015
Externally publishedYes


  • Heterochromatin
  • Lysine methyl transferase
  • Single molecule pull down and replication

ASJC Scopus subject areas

  • General Neuroscience
  • General Biochemistry, Genetics and Molecular Biology
  • General Immunology and Microbiology


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